The present invention relates to electron emission, particularly to patterned electron emitting devices, and more particularly to low work function, stable compound cluster generation and the patterned deposition thereof on surfaces whereby extraction of electrons and obtaining illumination is easily accomplished.
Visual displays of various types are being widely utilized. A considerable fraction of the total energy consumption in the United States and other technically advanced countries is spent in powering visual displays, such as televisions and computer monitors. Flat panel displays are increasing in popularity since they are light and small, and are becoming an integral part of visual displays, particularly since they are less bulky than conventional cathode ray tubes (CRTs). Liquid crystal displays are commercially available and are mainly used for portable computers. The disadvantages of the liquid crystal display include high energy consumption, high cost of production, low intensity, and difficulties associated with large diameter display production. Among a few alternatives to this technology is the field emission display. This type of display relies on the emission of electrons from an array usually made up of sharp tips. The ease of electron emission, and therefore the amount of energy consumed by the display, depends on the work function of the emitter material and the sharpness of the tips. The work function of a material is defined as the minimum energy needed to remove an electron from a material to a point at an infinite distance away outside the material's surface. The production of sharp tips and reliable low work function materials has not been achieved successfully and substantial effort has been directed to this problem. A low work function is considered to be &lt;3.5 electron-volts (eV). Recently, a process and apparatus have been developed which enables the deposition of low work function material on the field-emission tips and which is described and claimed in co-pending U.S. application Ser. No. 09/080,109, filed May 18, 1998, entitled "Low Work Function Surface Layers Produced by Laser Ablation Using Short-Wavelength Photons," assigned to the same assignee.
The present invention provides an alternative to the sharp tip electron-emission devices. The invention involves the production of compound clusters with small radius having low work function, which enables efficient electron-emission and illumination with low energy consumption and ease of fabrication. The low work function, stable silicon-based compound cluster generation, and their patterned deposition on surfaces enable their use, for example, as cathode material for field emission flat panel displays, electron guns, and cold cathode electron guns. The low work function compound clusters are produced by co-evaporation of solid semiconductor (i.e., Si) and alkali metal (i.e., Cs) elements in an oxygen environment, and can be easily patterned during cluster film deposition.